Description of Axial Detail for ROK Fuel

Trellue, Holly R¹  Galloway, Jack D¹ 

[1] Los Alamos National Laboratory

关键词: BURNUP;    COOLING TIME;    DECAY;    DISTRIBUTION;    FUEL ASSEMBLIES;    FUEL PINS;    GEOMETRY;    LANL;    METERS;    ORNL;    SIMULATION;    SPACERS;   

DOI  :  10.2172/1039310
RP-ID  :  LA-UR-12-20724
PID  :  OSTI ID: 1039310
Others  :  TRN: US1202184

美国|英语

来源: SciTech Connect

【 摘 要 】

For the purpose of NDA simulations of the ROK fuel assemblies, we have developed an axial burnup distribution to represent the pins themselves based on gamma scans of rods in the G23 assembly. For the purpose of modeling the G23 assembly (both at ORNL and LANL), the pin-by-pin burnup map as simulated by ROK is being assumed to represent the radial burnup distribution. However, both DA and NDA results indicate that this simulated estimate is not 100% correct. In particular, the burnup obtained from the axial gamma scan of 7 pins does not represent exactly the same 'average' pin burnup as the ROK simulation. Correction for this discrepancy is a goal of the well-characterized assembly task but will take time. For now, I have come up with a correlation for 26 axial points of the burnup as obtained by gamma scans of 7 different rods (C13, G01, G02, J11, K10, L02, and M04, neglecting K02 at this time) to the average burnup given by the simulation for each of the rods individually. The resulting fraction in each axial zone is then averaged for the 7 different rods so that it can represent every fuel pin in the assembly. The burnup in each of the 26 axial zones of rods in all ROK assemblies will then be directly adjusted using this fraction, which is given in Table 1. Note that the gamma scan data given by ROK for assembly G23 included a length of {approx}3686 mm, so the first 12 mm and the last 14 mm were ignored to give an actual rod length of {approx}366 cm. To represent assembly F02 in which no pin-by-pin burnup distribution is given by ROK, we must model it using infinitely-reflected geometry but can look at the effects of measuring in different axial zones by using intermediate burnup files (i.e. smaller burnups than 28 GWd/MTU) and determining which axial zone(s) each burnup represents. Details for assembly F02 are then given in Tables 2 and 3, which is given in Table 1 and has 44 total axial zones to represent the top meter in explicit detail in addition to the other 26 zones. Note that the MCNP files for F02 were created using the Monte Carlo burnup linkage code Monteburns, which saves MCNP input files with detailed compositions as a function of burnup. The 'intermediate burnup files' produced for F02 include a cooling time of 27 years. The axial location of 5 spacers was also included in the ROK F02 assembly in which each spacer contained a length of 3.81 cm. Note that due to the nature of Monteburns, which was run in a special fashion for this problem, the step number increments after the 27 year decay, so the second column of Table 2 refers to the step number that should be used in the Monteburns files.